Automatic control system



Oct. 23, 1945. A N N 2,387,604

AUTOMATI G CONTROL SYSTEM Filed May 28, 1941 zac 23B INVENTOR Alwim B.Nczwion... BY

ATTORNEY H I H I I Patented Oct. 23, 1945 AUTOMATIC CONTROL SYSTEM zuwaiB. Newton, Minneapolis, Minn., assignor to Min'neapolis-floneywellRegulator Company, LMinneapolis, Minn, a corporation of DelawareApplication May 23, 1941, .Serial No. 395,561

'17 Claims.

proved meansfor modifying the operation of a condition responsive switchor equivalent (the condition being pressure or temperature or the like)device in response to conditions at a plurali-ty of remote points.

Another-object is tocorrtrol theamount of com pressor operation inarefrigerating system having a plurality of -.evaporators in accordancewith the total refrigerating requirements of a plurality of spaces-beingserved.-

Another object to-adjustably bias a condition responsive switch E ymeans of an electromagnetic device, the energization-of which iscontrolled jointly by control instruments located at a plurality ofdifierent points.

Further objects andadvarntagesof my invention will become apparent fromthe following detailed description- .and annexed drawing, the singlefigare of which represents a refrigerating system -for a plurality ofcompartments, my invention being embodied the control arrangement forthe '1 system.

Referring to the'drawnig, a refrigeration system of the compression typeis shown, the system having a compressor motor controlled .by theparticular control arrangement constituting oneform of my invention.Numeral i designates the compressor which is driven by anelectric motorH through a belt 42 The compressor discharges into a condenser 13through a pipe 14 and the condenser 13 is connected to a plurality ofevaporators A, B, and NC by means of a pipe 16 having branches ISA, [6B,and 1-50 connected to the respective evaporators, the evaporators beingdisposed in separate compartments to be refri erated 18A, 18B and 18C.Numeral l9 designates the suction pipe of the compressor which hasbranches ISA, I93 and 190 connected to the outlets of the respectiveevaporators. Interposed in the supply pipes .I BA, IE3 and 160 arethermostatic expansion valves A, 15B and IEC re spectively. these valvesbeing of a well known type adapted to maintain a constant number ofdegrees of superheat at the outlets of their respective evaporators. Therespective valvesare connected tothermal bulbs 22A,22B and'22Cwhich areadj aann cent the outlets of the evaporators, by means ofcapillary'tubes 23A, 23B and 23C. The operation of these expansionvalves is well known in the art and need not be described in furtherdetail.

The controls .for the compressor motor include a controller designated.by the reference character 25 which comprises a generally rectangularmetal casing 2-6, .the casing having a flanged opening 21 as shown,through which electrical leads controlling the compressor motor -I Ipass to the interior of the casing.

Within the casing 26 is a horizontal shelf 29 having a portion 30forming a bracket which may be suitably secured to a side wall of thecasing 26. The shelf 29 is primarily supported by standards BI and 32upstanding from the bottom of the casing 26. Numerals .35 and 3Bdesignate bolts which extend through the standards 31 and 82 whichengage the shelf 29 in screw-threaded relationship. Supported on theshelf 29 is a, snap switch .31 :is enclosed within a Bakelite housingdetail in the application of Albert Baak, Serial No. 307,991, filed-onDecember '7, 1939. Thesnap switch 3'1 is enclosed within a bakelitehousing and has on and on positions and is of the type which tends toremain in the position to which it is opera-ted. The snap switch 31. hasan operating stem 38 extending downwardly therefrom, the stem 38 havingtwo spaced horizontal slots or openings therein. As shown, the snapswitch 31 has two contact terminals formed by screws 39 and 40 formaking electrical connections to the switch.

The operating mechanism for the snap switch 31 includes a, pressureresponsive bellows enclosed within a housing 41 at the lower portion ofthe casing 2-6. The housing 41 is flanged and the flange is secured tothe lower side of the casing 26 by .screws which include the screws 35and 42. The bellows within housing '4'! is eXDa-nsible and contractibleand is connected to the suction pipe of the compressor by a tube :43. Ifdesired the bellows could be actuated directly by evaporatortemperature. The operating end of the bellows operates a bellows post 44which extends through a nut 45 within the casing 26. The nut 45cooperates with a spring within housing M which opposes the bellows, andby adjusting the nut 45 the tension of the spring and correspondinglythe loading on the bellows may be varied. At the upper end of thebellows post 44 is a ball 46 loosely engaged within an opening in anoperating lever 41, the right end of which is engaged in the upmr one ofthe slots in the switch operating stem 38. Numeral 48 designates a leafspring secured at one end to the lever 41 by rivets or the like with theother end engaging the upper side of ball 46. Numeral 49 designates asimilar leaf spring secured to the opposite side of lever 41 and havingan opening through which the upper end of the bellows post 44 extendswith the leaf spring 49 engaging the lower side of the ball 46. Thearrangement just described forms a strain release connection between thebellows post 44 and the operating lever 41.-

The left end of the operating lever 41 is disposed between two cams 52and 53, each of which has a spiral contour. The cam 52 is mounted on ashaft which extends through a side wall of the casing 26 and which isrotatable by a manual knob 54 outside of the casing. Adjacent the knob54 is a dial 55 movable with respect to an index marker for indicatingthe position of the cam 52. The cam 53 is mounted on a shaft whichextends through a side wall of the casing 26 and which is rotatable by amanual knob 58 outside of the casing, and there is a graduated dial 51similar to dial 55 adjacent the manual knob 56.

From the foregoing, it will be seen that the lever 41 is a floatinglever and that it left end moves between the cams 52 and 53 which act asstops. The lever 41 is moved by the suction pressure affecting thebellows within housing 4|. When the suction pressure rises, the bellowswithin housing 4| is expanded and the bellows post 44 moves lever 41upwardly by reason of engagement of ball 48 with the leaf spring 48.When the left end of lever 41 engages cam 52, the cam acts as a stop forthe lever 41 and the lever 41 is then constrained to pivot in acounter-clockwise direction about the cam which acts as a fulcrum.Counter-clockwise movement of the right end of lever 41 moves theoperating stem 38 of switch 31 upwardly so as to move the switch toclosed position. When the switch 31 moves to closed position the circuitfor the compressor motor is completed as follows: from a line conductor68 through wire 6| to terminal 40 of the snap switch through the snapswitch to terminal 39, wire 62 through the compressor motor and throughwire 83 back to line conductor 64. The parts are normally so arrangedand adjusted so that switch 31 will be closed at suction pressure highenough to insure that the evaporator temperature has risen high enoughto defrost it after each cycle of the compressor. In the event thereshould be a rise in suction pressure when the snap switch is closed, asdescribed, upward movement of the ball 46 with respect to lever 41 ispermitted by virtue of the resiliency of the leaf spring 48. The point,that is the pressure, at which lever 41 will begin to move in acounterclockwise direction so as to close the snap switch may beadjusted by rotatably adjusting the cam 52 which, as pointed out above,has a spiral contour so that the point of engagement between its edgeand the end of lever 41 may be raised and lowered by rotating the cam.After the compressor has started in operation the suction pressure willfall causing the bellows within housing 4| to contract, thereby movingthe bellows post 44 downwardly until the left end of lever 41 engagescam 53. When this happens the lever 41 will pivot in a clockwisedirection about the cam 53 which acts as a fulcrum, the right end oflever 41 moving downwardly so as to move the operating stem 38downwardly to open the snap switch 31. The pressure at which lever 41will thus move in a clockwise direction for opening the switch andstopping the compressor may be adjusted by adjusting the position of cam53 which also has a spiral contour, as pointed out above, that is, thepoint at which lever 41 engages the edge of the cam may be raised andlowered by rotatably adjusting the cam.

The snap switch 31 may also be operated by a device responsive to thedischarge pressure of the compressor. This device includes an expansibleand contractible bellows enclosed within a housing 85 which has a flangesecured to the lower side of the casing 26 by screws 66 and 61. Thebellows within housing 85 is connected to the discharge pipe M of thecompressor by a tube 68. The bellows within housing 65 operates abellows post 69 which extends through a nut 18 inside of the casing 26.The nut 18 cooperates with a spring within housing 65 which opposes thebellows therein, and by adjusting the nut 10 the tension of the springand correspondingly the loading of the bellows within housing 65 can bevaried. Numeral 1| designates a small lever having ears pivotallyengaging a pin 12 extending outwardly from the back of the casing 26.The right end of lever 1| is engaged in the other of the slots in theoperating stem 38 and the left end of the lever 1| may be actuated by ascrewthreaded member 14 carried by the end of the bellows post 69; thatis, when the compressor discharge pressure increases to a predeterminedrelatively high value, the bellows within housing 65 expands movingmember 14 into engagement with lever 1| causing lever 1| to rotateclockwise so as to move operating stem 38 downwardly opening snap switch31 the snap switch may be thus opened even though the suction pressureis at a value at the time to have the switch closed. The strain releaseconnections between bellows post 44 and lever 41 will permit theoperating stem 38 to be moved downwardly by the discharge pressureresponsive device even though the lever 41 is engaging cam 52 at thetime, the leaf springs 48 and 49 permitting relative movement of lever41 and the ball 46 as pointed out above.

The structure so far described has heretofore been used in the art forcontrolling a compressor in response to suction pressure and headpressure. My invention comprehends employing additional mechanism inconjunction with the controller whereby the compressor is controlled inresponse to the temperature within the refrigerated compartments aswell.

Numeral 18 designates an electromagnetic device comprising a winding 19supported by means of a bracket extending outwardly from the side of thecasing 26. The winding 19 has an armature 8| cooperating therewith, thelower part of which carries a member 82 having a knife edge 83. Thenumeral 84 designates a lever having a boss 85 which normally engagesthe underside of shelf 29, the right end of the lever extending throughan opening in the side of the casing 28 and the right end of the leverhaving a crimped portion 86 as shown which engages the knife edge 83 sothat the lever 84 may pivot about the member 82. The left end of thelever 84 has a finger 81 normally engaging the leaf spring 48 directlyabove the ball 46 so that downward force exerted by the left end oflever 84 is in line with the force exerted through bellows post 44 andis directly opposed thereto. The right end of lever 84 is normally urgedinto engagement with the knife edge 83 by a coil spring 88, the upperend of which is attached to an ear 89 on lever 84 and the lower end ofwhich is attached to a member 90 engaged on a screw 9! extending througha bracket 92 extending outwardly from the side of the casing 26. Thetension of spring 88 may be adjusted by adjusting the screw 91. Numeral93 designates a guide member attached to member 98 which moves in aslotinthe side of casing 26.

The winding 19 of the device 18 normally oarries a certain amount ofcurrent, and its mag netic field urges the armature 81 in an upwarddirection with a force depending upon the amount of current flowingthrough the winding 19. The upward force exerted on the right end oflever 84 tends to cause lever 84 to fulcrum about the point at whichboss 85 engages the shelf '29, the left end of lever 84 exerting a forceas described above opposing that of the bellows within ho11s ing 4!actin through the bellows post 44. In

other words, the device 18 provides a resistance to upward movement oflever 41 and closure of switch 31 which raises the cut-in point of theswitch an amount depending upon the energizetion of winding 19. In otherwords, when lever 41 is moved upwardly so as to engage cam 52 for,

closing the snap switch 31, the lever 84 must be rotated slightly in aclockwise direction against the upward pull exerted on its right end bythe armature 85. On the other hand, when the suction pressure isdecreasing, the device 18 assists downward movement of lever 4'! andraises the cut-out point of switch 3! by a similar amount depending uponthe energization of winding 19.

Winding 19 is controlled by an electric circuit which extends through aresistance type thermostat disposed in each of the compartments 18A, 18Band 18C, these thermostats being designated by the reference characters95A, 95B and 95C, respectively. The thermostat 95A comprises anexpansible and contractible bellows 96A containing a volatile liquid.the movable end of the bellows having a stem which engages a pivotedslider or arm 91A, the left end of which slides over an electricalresistance 98A. The slider 91A is normally biased in a counter-clockwisedirection by a coil spring 99A. When the temperature in compartment ISArises, the bellows 96A expand moving the end of slider 81A upwardlyalong resistance 98A and increasing the resistance in circuit withwinding 19 as will presently appear. When the temperature in compartmentlBA decreases, the bellows 96A contacts moving the slider 91A downwardlyalong resistance 98A.

The thermostats 95B and 95C are identical with thermostat 95A and theelements of these thermostats are designated by the same numerals withidentifying letters 50 that these thermostats need not be furtherdescribed.

Numeral I designates a high limit thermostat in the compartment l8Awhich comprises a normally closed switch which is opened when thetemperature in compartment lBA rises to a relatively high value beyondwhich it is not desired that the temperature rise. Numeral lflldesignates a low limit thermostat comprising a normally opened switchwhich closes when the temperature in compartment 480 falls to arelatively low value below which it is not desired that the temperaturein compartment 180 should go. Numeral 102 designates a single-pole,doublethrow manual switch comprising a switch arm I03 and terminals I84and IE5, the purpose of which will be described presently.

The winding 19 is normally energized through an electrical circuit asfollows: from wire W8 through winding 719. wire 18!], wire H0, part ofresistance 98C, slider 97C, wire I, wire H2, part of resistance 98B,slider 91B, wire H3, part of resistance 98A, slider 91A, wire H4, wire5, high limit thermostat 108 to wire 416, the wires I08 and I 16 beingconnected to a suitable source of power not shown. From the foregoing,it is apparent that the energization of winding 19 depends upon theamount of current flowing there through which is determined by thepositions of thermostats 91A, 91B and 91C, that on the amount ofresistance in the circuit of the winding. When the temperatures in thecompartments I8A, 18B and I are at predetermined values, the thermostatshave their sliders 91 at the mid points of their respective resistancesas shown. Under these olrcmnstances, the winding 19 carries apredetermined current, and its energization provides a predeterminedforce acting through lever 84 to oppose the bellows within housing 4|.Thus, the normal cut-in and cut-out points of the switch 31, as earlierdetermined by the settings of cams 52 and 53, are raised a predeterminedamount as described above determined by the energization of winding 18.The compressor will now be started and stopped at suction pressurescalculated to produce sufficient compressor operation to meet therequirements of all of the compartments l-8A, RB and 180. As thetemperature in any compartment rises above the desired value, itsrespective thermostat will move its slider upwardly along its respectiveresistance thereby increasing the amount of resistance in circuit withwinding 19 so as to thereby decrease the energization of the winding.Upon this occurring, the upward force exerted on armature 8| will bedecreased and correspondingly the downward force exerted by finger 81opposing upward movement of bellows post 44 will be reduced. Thus, therewill be less resistance offered to expansion of the bellows withinhousing 41 and the left end of the lever 41 will engage cam 52 at alower pressure than previously, and the switch 31 will be closed at thislower pressure. In other words, the compressor will now be cut in soonerthan before to meet the increased cooling requirements. Likewise. thecut-out point of switch 31 will be correspondingly lowered due to thereduced downward force exerted by the left end of lever 84, that isthere will be less force assisting the downward movement of lever 41towards the cam 53. Whenever there is a decrease in temperature in anyof the compartments [8A, IBB or I80. the thermostat of that compartmentwill move its respective slider downwardly along its associatedresistance, thereby decreasing the resistance in circuit with winding 19and increasing the energization there of. Thus, the armature 8| will bepulled upwardly with increased force and the finger 81 of lever 84 willexert an increased downward force in bellows post 44. The suctionpressure will now have to rise a higher value than originally in orderto overcome this increased force to bring about the closure or theswitch 31,. Similarly. the increased downward force exerted by the leftend of lever 84 will correspondingly raise the cut-out point of switch31.

From the foregoing, it is to be seen that when there is an increase intemperature in any compartment, the compressor will .be cut in at alower value of suction pressure; that is, after it has been stopped itwill be started normally after a shorter delay than usual. Also, whenthere has been a rise in temperature in any compartment, the compressorwill be shut down at a lower suction pressure, or in other words it willoperate longer than normally. It is to be seen therefore that when thereis a need for increased refrigeration the on cycles of the compressorare increased in length of the off cycles are shortened, the operationof the compressor being through a lower range of suction pressure. Whenthere is a demand for reduced refrigeration in any compartment, therelative duration of the compressors on and off cycles is variedoppositely; that is, the on cycles are reduced in length and the offcycles are lengthened. The thermostats 91 of all the compartments aresimultaneously eflective of course to control the electromagnetic deviceI8, and its energization depends upon the cumulative effect of allthermostats so that the operating pressures of switch 31 depend upon thetemperatures in all the compartments and consequently the amount ofcompressor operation. and the pressures at which it takes place dependsu on the requirements of all the compartments. Thus, the amount ofcompressor operation is governed in accordance with the total amount ofrefrigeration required.

Normally the temperatures in the various compartments will generallytend to rise and fall together in accordance with the on and off cyclesof the compressor, that is. the temperature in all the compartmentstending to fall when the compressor is operating so as to be raising thecut-out setting while the compressor is operating. Generally thetemperature will have risen in all the compartments before thecompressor starts and the controls may be so arranged that normally allthe evaporators defrost before the compressor starts.

In the event that the temperature in compartment I8A should rise to thesetting of the high limit thermostat I00, this thermostat will open andinerrupt the circuit of winding I9. This will of course completelydeenergize the winding I9 releasing the right end of lever 84 so that nopressure is exerted downwardly by finger 81 at the left end of lever 84.Thus, there will be no additional loading applied to the controller 26and it will operate at pressures determined by the settings of cams 52and 53. In other words, the cut-in. and cut-out points of switch 3'lwill be at their lowest respective values depending upon the settings ofcams 52 and 53 at the time. Thus, the amount of refrigeration producedwill be a maximum for the existing settings of cams 52 and and thisamount of refrigeration should normall be sufiicient to prevent thetemperature in compartment I8A from rising appreciably above the settingof thermostat I00. A high limit thermostat similar to thermostat I00 canof course be placed in each of the compartments in series with thewinding 19.

Referring to the low limit thermostat IOI in compartment I80, when thetemperature in this compartment falls to a relatively low value forwhich the thermostat is set this thermostat will close, completing acircuit through winding I9 which shunts all of the thermostats 95 whenmanual switch. I02 is in the position shown. This circuit is as follows:from wire I08 through winding I9, wire I09, wire I20, terminal I04,blade I03, wire I2I, thermostat IOI, wire I22, wire II5, thermostat I00,and wire II6. This circuit does notinclude the resistances of thethermostats 95 and thus the amount of current flow through winding 19,and its energization will therefore be all at a maximum.correspondingly, the amount of downward force exerted by finger 81 inline with bellows post 44 will be at a maximum and the cut-in andcut-out points of switch 31 will now beat their maximum values for theexisting settings of cams 52 and 53. Thus, the amount of refrigerationproduced will be at a minimum so as to prevent the temperature incompartment I00 from further falling below the setting of thermostatIOI.

If desired, the manual switch I02 may be moved to its other positionwherein blade I03 engages terminal I05. With the manual switch sopositioned only the thermostats A and 95B are shunted, the circuitthrough the low limit thermostat and through winding I9 now being asfollows: from wire I08, through winding I9, wire I09, wire IIO, part ofresistance 98C, slider 91C, wire III, wire I23, terminal I05, switchblade I03, wire I 2|, thermostat I 0|, wire I22, wire II5, thermostatI00 and wire IIG. Inasmuch as this circuit shunts the thermostats 95Aand 95B, the resistance in circuit with winding I9 is substantiallyreduced and its energization correspondingly increased to raise thecut-in and cut-out points of the switch 31 and reduce the amount ofrefrigeration in the same manner as explained above. If desired, a lowlimit thermostat similar to thermostat IOI and similarly wired might beplaced in each of the other compartments I8A and I8B. I

From the foregoing, those skilled in the art will readily appreciatethat I have provided a control arrangement for a multiple evaporatorsystem wherein thecompressor is conveniently and advantageouslycontrolled primarily in re sponse to suction pressure. with the amountof compressor operation being varied dependently upon the amount ofrefrigeration required of the evaporators. The apparatus utilized issimple in construction and trustworthy in operation, not requiringcomplicated or delicate parts. The control arrangements are such thathigh and low limit thermostats may very conveniently be made of use inany or all compartments to be refrigerated.

The single embodiment of my invention which I have disclosed isillustrative of its preferred form although many variations andmodifications therein will occur to those skilled in the art. Mydisclosure is therefore to be interpreted in an illustrative rather thana limiting sense, and the scope of my invention is to be determined onlyin accordance with the claims appended hereto.

I claim as my invention:

1. In apparatus of the character described, in combination, an automaticcontrol device comprising a movable element, pressure operable means foractuating said element, means resisting movement of said element, andspace temperature responsive means associated with said resisting meansfor varying the resistance offered to movement of said element, saidspace temperature responsive means comprising an electromagnetic deviceassociated with said element and means for proportionately varying theenergization of said device in accordance with temperature changes.

2. In apparatus of the character described, in combination, an automaticswitch having an operating member, pressure actuatable means for movingsaid member, temperature changing means controlled by said switch, meansfor biasing said operating member comprising an eleca HUMIDITYREGULATION.

tromagnetic device and thermostatic means responsive to the temperaturein a space for proportionately varying the energization of said devicefor modifying the bias of said member in accordance with temperaturevariations in the space.

3. In apparatus of the character described, in combination, an automaticswitch having an operating member, pressure actuatable means for movingsaid member, temperature changing means for a plurality of spacescontrolled by said switch, means for biasing said operating membercomprising an electromagnetic device and a plurality of thermostats, onein each space for varying the energization of said device for modifyingthe bias of said member.

4. In a refrigerating system, in combination, a compartment to berefrigerated, an evaporator in said compartment, means including acompressor for circulating refrigerant through said evaporator, switchmeans including an operating member controlling said compressor,pressure actuatable means for moving said member, means for biasing saidoperating member, said last means including an electromagnetic device, athermostat in said compartment arranged to proportionately vary theenergization of said device in accordance with temperature changeswhereby the bias of said switch operating member is varied so as tocontrol the amount of compressor operation in accordance withrefrigeration requirements.

5. In a refrigerating ystem, in combination, a plurality of compartmentsto be refrigerated, an

evaporator in each compartment, means includ- I ing a common compressorfor circulating refrigerant through said evaporators, switch meansincluding an operating member controlling said compressor, pressureactuat'able means for moving said member, means for biasing said operating member, said last means including an electromagnetic device, athermostat in each compartment, means whereby said thermostats jointlycontrol the energization of said device whereby the bias of said switchoperating member is varied so as to vary the amount of compressoroperation in accordance with the total refrigeration requirements.

6. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means including an operatin member controllingsaid compressor, pressure actuatable means for moving said member, meansfor biasing said operating member, means for controlling the biasexerted by said biasing means including a thermostat in eachcompartment, the thermostats being arranged to jointly vary the bias ofsaid switch operating member to control the amount of compressoroperation in accordance with the total refrigeration requirements.

7. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means includin a common compressor for circulating refrigerant throughsaid evaporators, switch means including an operating member controllingsaid compressor, pressure actuatable means for moving said member, meansfor biasing said operating member, said last means including anelectrical device responsive to the amount of current flowingtherethrough, a variable resistance type thermostat in each compartment,said thermostats being arranged to jointly control the energization ofsaid device, whereby the bias of said switch operating member is variedso as to vary the amount of compressor operation in accordance with thetotal refrigeration requirements.

8. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means, including an operating membercontrolling said compressor, pressure actuable means for moving saidmember, means for biasing said operating member, said last meansincluding an-electrical device responsive to the amount of currentflowing therethrough, a variable resistance type thermostat in eachcompartment, said thermostats being arranged to jointly control theenergization of said device whereby the bias of said switch operatingmember is varied so as to vary the amount of compressor operation inaccordance with the total refrigeration requirements, and a, thermostatresponsive to a predetermined temperature in one of said compartmentsassociated with said device for substantially changing the energizationof said device to vary the bias of said switch operatin member and theamount of compressor operation accordingly.

9. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means including an operating member controllingsaid compressor, pressure actuatable means for moving said member, meansfor biasing said operating member, said last means including anelectrical device responsive to the amount of current flowingtherethrough, a variable resistance type thermostat in each compartment,said thermostats being arranged to jointly control the energization 'ofsaid device whereby the bias of said switch operating member is variedso as to vary the amount of compressor operation in accord- I ance withthe total refrigeration requirements,

and a thermostat responsive to a relatively high temperature in one ofsaid compartments controlling said device for substantially changing theenergization thereof to vary the bias of said switch operating member ina direction to substantially increase the amount of compressoroperation.

10. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means including an operating member controllingsaid compressor, pressure actuatable means for moving said member, meansfor biasing said operating member, said last means including anelectrical device responsive to the amount of current flowingtherethrough, a variable resistance type thermostat in each compartment,said thermostats being connected in series with said device for jointlycontrolling the energization thereof whereby the bias of said switchoperating memher is varied so as to vary the amount of compressoroperation in accordance with the total refrigeration requirements.

11. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means ineluding an operating member controllingsaid compressor, pressure actuatable means for moving said member, meansfor biasing said operating member, said last means including anelectrical device responsive to the amount of current flowingtherethrough, a variable resistance type thermostat in each compartment,said thermostats being connected in series with said device for jointlycontrolling the energization thereof whereby the bias of said switchoperating member is varied so as to vary the amount of compressoroperation in accordance with the total refrigeration requirements, and athermostat in one of said compartments responsive to a predeterminedtemperature therein for interrupting the circuit of said device tosubstantially decrease the energization of said device for varying thebias of said switch operating member and the amount of compressoroperation correspondingly.

12. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means including an operating member controllingsaid compressor, pressure actuatable means for moving said member, meansfor biasing said operating member, said last means including anelectrical device responsive to the amount of current flowingtherethrough, a variable resistance type thermostat in each compartment,said thermostats being connected in series with said device for jointlycontrolling the energization thereof whereby the bias of said switchoperating member is varied so as to vary the amount of compressoroperation in accordance with the total refrigeration requirements, and athermostat in one of said compartments responsive to a predeterminedtemperature therein for shunting at least one of said aforementionedthermostats to substantially increase the energization of said devicefor varying the bias of said switch operating member and the amount ofcompressor operation corresponde y.

13. In a refrigerating system, in combination, a plurality ofcompartments to be refrigerated, an evaporator in each compartment,means including a common compressor for circulating refrigerant throughsaid evaporators, switch means including an operating member controllingsaid compressor, pressure actuatable means for moving said member inresponse to suction pressure for producing cycling operation of thecompressor,

means for biasing said operating member, means member to control thecut-in and cut-out points of said switch means, the temperatures in thecompartments normally rising to defrosting values of the evaporatorsduring ofi cycles of the compressor and the thermostats lowering thecutin point of the switch means, the thermostats acting to raise thecut-out point of the switch means as the compartment temperatures fallduring operation of the compressor.

14. In a system of the class described comprising in combination, aplurality of spaces whose temperature is to be controlled, cooling coilsin said spaces, a refrigeration system comprising compressor means andcondenser means for supplying refrigerant to said coils, means formaintaining the suction pressure of said refrigerant between definitevalues, and means for changing said values in accordance with thetemperature in each of said spaces.

15. In a system of the class described comprising in comblnation, aplurality of spaces whose temperature is to be controlled, cooling coilsin said spaces, a refrigeration system comprising compressor means andcondenser means for supplying refrigerant to said coils, means formaintaining the suction pressure of said refrigerant between definitevalues, electrical means for biasing said maintaining means, and meansfor varying the flow of current through said electrical means inproportion to the temperature changes in each space for varying saidvalues.

16. A system of the class described, comprising, in combination, aplurality of spaces whose temperature is to be controlled, means forsupplying a temperature changing fluid to said spaces, means acting onsaid fluid to cause it to change the temperature of said spaces, meansresponsive to a condition related to the temperature of said fluid forcontrolling said last named means to maintain said condition betweendefinite values, and means for changing said values in accordance withthe temperature in each of said spaces.

17. A system of the class described, comprising, in combination, aplurality of spaces whose temperature is to be controlled, means forsupplying a temperature changing fluid to said spaces, means acting on.said fluid to cause it to change the temperature of said spaces, acontroller responsive to a condition related to the temperature of said'fluid for controlling said last named means to maintain said conditionwithin predetermined limits, electromagnetic means associated with saidcontroller in a manner to bias it and hence vary said limits, and meansfor varying the flow of current through said electromagnetic means inaccordance with the change of temperature in each of said spaces.

ALWIN B. NEWTON.

CERTIFICATE OF CORRECTION. Patent No. 2,587,6ou. October 25, 19L 5QAININB. NEWTON.

It is hereby certified that error appears in the printed Specificationof the above numbered patent requiring correction as follows; Page 1,sec 0nd column, line 21, for "is enclosed within a Bakelite housing"read --which is of the same type disclosed in -g and that the saidLetters Pat wnt should be read with this correction therein that thesame may conform to the record of the case in the Patent Office.a

Signed ahd sealed this 22nd day of January, A. D. 19146,

Leslie Frazer (Seal) First Assistant Commissioner o Patents

